Which law reorganized the civil service?

The reorganization of the U.S. civil service was primarily addressed by the Civil Service Reform Act of 1978. This landmark legislation established the Office of Personnel Management (OPM), introduced merit-based hiring and promotion, created the Senior Executive Service (SES), and established the Merit Systems Protection Board (MSPB). These reforms aimed to enhance the efficiency, fairness, and professionalism of the federal government's workforce.